Copied from an early 1800s crescent-shaped table fork and boxes which are designed to be surface-mounted on the underside of a table. To buy the fork only, the reduction in price is shown below.
Centre of Prong to Centre of Prong: 2 1/4" (57mm)
Thickness of Prong: 1/8" (3mm)
Note: Main image is view from underside of clip - surface mounted boxes.

Copied from a good quality Georgian cranked table fork with boxes. The boxes, tensioned with springs , are designed to be inset in the underside of the table. To buy the fork only, the reduction in price is shown below.
Centre of Prong to Centre of Prong: 3 1/16" (77mm)
Thickness of Prong: 3/16" (4mm)
Note: Main image is view from underside of clip - boxes are inset.